The present invention generally relates to a control system for detecting the presence of a railcar along a length of track. More specifically, the present invention relates to a presence detector that includes a plurality of magnetic field sensors that each detect the presence of a railcar on a length of track and includes components for calibrating the output signal from each of the magnetic field sensors to adjust for the earth's magnetic fields in the location near the magnetic field sensor.
Since the inception of railroads, the control of trains along tracks, and specifically along the multiple parallel, closely spaced tracks typically included in rail yards, has been a priority and concern to prevent injury and damage. Part of the process of controlling the movement of trains through a rail yard requires the need for the automatic detection of railcars along each two-rail track included in the rail yard. Since many switching and arresting devices are automatically controlled in a rail yard, identifying the presence of railcars along the individual tracks is imperative to prevent collision and derailment.
Early detection devices oftentimes utilized pressure switches that operated upon movement of a track section due to the train weight and/or electrical contact switches that are operated through conduction of the train wheels. Although these prior systems provided some type of indication of a railcar presence, the systems included numerous drawbacks, which are primarily focused upon the operation of the pressure or conductive switches utilized along the length of the rail.
Another type of detector that has also been used to detect railcars within a rail yard utilizes photoelectric detectors to detect the presence of a railcar along a length of track. Although photoelectric detectors operate well in perfect conditions, the detectors oftentimes need to be calibrated or cleaned to remove dirt or snow that can block the photo detectors.
A presently available and commonly utilized railcar detector utilizes a continuous inductive coil buried beneath the rail track that includes multiple windings of an electrically conductive material. As the railcar passes over the coil of wire, the changing magnetic field created by the ferromagnetic material from the railcar changes the electrical current generated within the inductive coil. Thus, a change in the voltage from the inductive coil resulted in a train presence signal. Although this type of train detector system works fairly well, damage to any portion of the inductive coil results in failure of the entire detection system. Following such damage, repair personnel must initially identify the damage to the coil and subsequently replace the damaged area. The identification and repair of the damaged section of the sensing coil required both highly trained personnel and a significant amount of down time within the rail yard.
Therefore, a need exists for a railcar presence detector that is both robust and easily repairable to detect the presence of railcars along rail tracks within a rail yard. A need exists for such a system that can both accurately detect the railcar and provide a failsafe mode of operation to prevent damage and/or derailment of railcars within the rail yard.